Abstract
Consideration of the conditions existing within the turbulent zone formed by a free disperse jet mixing with fluid at rest surrounding it, leads to the conception of an equation for the mean velocity of the jet in an axial direction. Combining the latter equation with that for the upward drift velocity of the gases in a furnace, an expression is obtained for the trajectory of an overfire, or secondary air jet, projected into the furnace. By a similar process the method is extended to the case of a flame jet, taking into account its acceleration due to buoyancy.
The mechanism of combustion is next considered, commencing with an examination of the factors controlling the position of the ignition point in a flame jet, and the derivation of an expression for its location in a powdered-fuel flame. This is followed by the development of a formula for the burning rate of powdered fuel suspended in air, which when combined with that for the mean velocity in a flame jet, enables a relationship to be established between the flame length and the particle size, for the ideal case of a uniform powder. Subsequently, the grading or non-uniform nature of actual powders is taken into account. A method is also described for plotting a flame characteristic, showing the effect of fineness of grinding, turbulence, and burner design on the losses due to unburnt combustible.
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