Abstract

In the present paper, contact heat transfer on a batch-operated single circular floor of a multiple hearth furnace is numerically examined using the Discrete Element Method (DEM). The particles are agitated on the floor by a single rabble arm equipped with mixing blades. Two different rabble arm configurations are studied, a rabble arm with three blades covering just the area from the centre of the floor to the wall enclosing the circular floor, and a rabble arm with six blades, which covers the whole diameter of the floor. The floor temperature is set to 100°C, and the initial particle temperature is 20°C. Spherical particles made of aluminium and polyoxymethylene (POM) with two particle diameters (10 and 20 mm) are examined. Blade angle inclination is varied, namely, 0°, 45° and 90°. The major results are that for POM spheres the major mechanism dominating contact heat transfer is the gas layer in the vicinity of the contact point particle-floor, whereas for aluminium the heat transfer through the direct contact point of floor and particle is of equal importance as the heat transfer through the gas layer. For the first configuration with three blades, a larger blade angle leads to lower heat up rates, while the second configuration with six blades, increases the heating rate for larger blade angles.