Impact of bed motion on the wall-to-bed heat transfer for powders in a rotary kiln and effect of built-ins. (October 2021)

• Record Type: Journal Article
• Authors: Moumin, Gkiokchan; Tescari, Stefania; Sattler, Christian
• Is Part Of: International journal of heat and mass transfer. Volume 177(2021)
• Publication Date: 2021-10
• Subjects: Rotary kiln -- Granular -- Powder -- Lifter -- Rolling; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2021.121473
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Heat transfer analysis in rotary kiln without and with longitudinal strips. Heat transfer enhancement of powder by a factor of 2–3 with strips. Usage of 6 or 12 strips shows the same impact. Thermocouple response time and convectional losses main impact on measurements. Abstract: This study analyses experimentally the heat transfer from the wall to the particle bed in a rotating drum with and without addition of built-ins for improving the mixing of the powder. Two types of materials were employed, sand as a granular material ( d p, mean = 200 μ m ) and cement raw meal as a powdery material ( d p, mean = 15 μ m ) . A rotating cylinder heated through the outer shell was operated in batch mode, with rotational speeds of 1, 2 and 3 rpm and fillings of 5 and 10 %. The sand achieved a rolling motion, which makes the measured heat transfer coefficient predictable with theoretical models. At the contrary, cement raw meal showed very little mixing in a cylinder without built-ins and the measured heat transfer coefficient was much lower than the model predictions. Using longitudinal strips along the wall caused the powder to collapse regularly, increasing its heat transfer by a factor of 2–3, up to the range of predictions from theoretical models. Thus, a motion comparable to the rolling motion can be established with such built-ins which only cause limited dust formation. Furthermore, the limitations of the measurement method with rotating thermocouples are pointed out which mostly stem from the thermocouple response time and convectional losses, which are increased once built-ins are employed. Graphical abstract: Image, graphical abstract