Wall Heat transfer correlation for rotary kiln with secondary air flow and recycled materials inlet

International audienceThe increasing use of the baffled-rotary kiln equipment in many innovative materials processing industrial applications suggests examining the heat transfer phenomena in order to improve the multi-phase flow modeling. Their development and use will be relevant for tackling the current energy issues. The heat transfer models available for the rotary kiln in the literature are, for now, not enough efficient for the baffled-rotary kiln case. The present paper is aimed at suggesting a wall heat transfer correlation for the rotary kilns with 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 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 materials. Their analysis suggest a more appropriate physical modeling of the wall heat transfer path leading to transform the classical correlation of type Nu=f(Re,Pr) in a new expression of type Nu=f(Re,St) based on a inventory corresponding to the hot and cold fluxes flowing within the baffled-rotary kiln. Thus, the introduction of the Stanton number (St) in the wall heat transfer correlation is compared with the experimental Nusselt numbers calculated from the inner heat transfer coefficients measured in the large-scale baffled-rotary kiln. This expression is found more convenient for the baffled-rotary kiln application