Influence of operational parameters and material properties on the contact heat transfer in rotary kilns

The heat transfer by contact between the covered inner wall surface and the solid bed in a rotary kiln was experimentally investigated. An indirect heated batch rotary drum with a diameter of D = 600 mm and a length of L = 450 mm has been used. Inside the drum, a rotating and stationary measuring rod was installed, each assembled with 16 k-type thermocouples to measure the temperatures. Thus, the radial and circumferential temperature gradients within the solid bed were measured, and the contact heat transfer was determined from the heating of the bed. The effect on the contact heat transfer coefficient was estimated for the operational parameters of the drum, rotational speed (1, 3, 6 rpm) and filling degree (10%, 15%, 20%); the solid bed parameters, particle diameter (0.7, 1.3, 2.0 mm) and thermo physical properties (conductivity, heat capacity, density). As test material, quartz sand, glass beads and copper beads were used. The measured heat transfer coefficients were compared with theoretical calculations of four model approaches from the recent literature. A good agreement with just one of these model approaches could be achieved.