Experimental analysis of the flight design effect on the temperature distribution in rotary kilns

•Influence of the flight design on the temperature drop during cooling is measured.•Higher number of flights can decrease the cooling time by one third.•Increasing flight length ratio (FLR) up to 1 leads to better cooling.•Exceeding FLR of 1 worsens the cooling.•Particle motion-based explanations are given for the described influences. An experimental parameter study in an indirectly heated rotary drum (L = 1.76 m, D = 0.5 m) with L-shaped flights was conducted. The influence of the flight design parameters as the flight length ratio (0.375–2.0) and the number of flights (6–18) on the temperature-time profile and the temperature drop are analyzed. Therefore, the rotary drum is filled with glass beads as reference material and heated in batch operation while contact heat transfer is the main heat transfer mechanism. After reaching an upper temperature of 330 °C, the system is cooled by forced convection as ambient air is sucked through the drum. Type k-thermocouples in three axial and six radial positions are used to measure the time evolution of the temperature. The thermocouples are mounted to a flight, such that they rotate with the drum and also capture the circumferential temperature distribution.