A wall heat transfer correlation for the baffled-rotary kilns with secondary air flow and recycled materials inlet

The present paper is aimed at suggesting a wall heat transfer correlation for the rotary kilns with the secondary inlet. The experimental thermal data acquired within large-scale rotary drum applied to the asphalt concrete materials production, are remained in order to give rise the new issues. These latter results are connected to a visualization campaign performed at the pilot-scale in order to assess the transversal distribution of the granular phase materials. Their analysis suggests a more appropriate physical modeling of the wall heat transfer path. It leads to transform the classical correlation of type Nu = f(Re, Pr) in a new expression of type Nu = f(Re, St) based on a new physical modeling inventory corresponding to the hot and cold fluxes flowing within the baffled-rotary kiln. Thus, the major modification is based on the introduction of the Stanton (St) number in the wall heat transfer correlation. This expression is found more convenient for the baffled-rotary kiln application. This new expression is validated by the comparison with the experimental Nusselt numbers calculated from the inner heat transfer measurements coefficient measured in the baffled-rotary kiln performed at large scale.