Transverse particle motion analysis as a basis for heat transfer investigations in rotary kilns with flights. Part II: Influence of operational parameters on heat transfer surfaces

The knowledge about quantitative heat transfer processes in rotary kilns is important in order to achieve an optimal product quality. To determine the heat transfer, the corresponding surfaces, as well as the hydraulic cross-sectional area are necessary to know. Three surfaces are essential for the heat transfer; the covered rotary wall, the free rotary kiln wall and the surface between the free packed bed and gas phase. Flights are very beneficial to reduce segregation effects, but also to increase the heat transfer as the contact surface between particles and gas phase is increased through the creation of falling particle curtains. In Part I of this investigation, the experimental setup and the determination of the relevant parameters required to quantify the inner and outer curtain surface were presented. This paper highlights the influence of material and operating parameters on the heat transfer surfaces. It is shown that the inner curtain surface increases with rotational speed due to the higher particle discharge rate. Increasing the filling degree above the optimum reduces the inner curtain surface because of the decreasing particle fall height. Larger particle diameters result in smaller inner curtain surfaces, while the outer curtain surface is mainly affected by the filling degree.