This paper will present the results of an investigation of theoretical models of atomization which can be used for a phenomenological theory for coal slurry atomization. This investigation was conducted in three areas. An intensive analysis of the rheological properties of coal slurry fuels was performed including viscosity as a function of shear rate, the extensional viscosity, and the viscoelastic properties. In order to evaluate atomization over a sufficiently wide range of rheological properties simulated fluids consisting of corn syrup and water and baseline Newtonian fluids were studied. Another area was the atomization of both coal slurries and simulated fluids under a variety of spray conditions using a Malvern Size Analyzer. Three basic theoretical models were analyzed to determine the best approach to characterizing these complex fluids. One model was a linearized Navier Stokes equation for a cylindrical fluid stream breaking up into drops under the impact of a high velocity air stream. A second model was a collisional model by which the collision of the air stream and the fluid stream produced droplets. Energy and momentum conservation were used to derive relationships between the drop size and the relevant physical parameters. A third model studied was a statistical model using a Boltzmann-type transport equation for the propagation of drops under the interactions of a high velocity airstream. The effects of drop coalescence and breakup are incorporated into this model. By comparing the various theoretical models with the atomization data and the rheological data a phenomenological model was constructed which correctly predicted the trends of the Sauter mean Diameter as a function of air/fuel ratio, rheological properties and spray angle. An effective viscosity was defined which included the effects of viscous losses, extensional properties, and viscoelastic properties. In addition, the effects of yield point were incorporated and shown to be important in predicting atomization properties.
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