Thermal Fluctuations and Heat Transfer Measurements in an Externally Heated Rotary Cylinder

Rotary cylinders are widely used in the industries for thermal processing of granular materials. It is highly important to maintain the uniform temperature throughout the solid bed during this process. In the current study, the temperature fluctuations in the bed and the wall to bed heat transfer coefficients (HTC) are estimated. A pilot plant rotary steel cylinder of length 45 cm and internal diameter of 60 cm has been designed and fabricated with industrial norms. Two rods, each assembled with 16 thermocouples of k-type are arranged in the cylinder, one fixed and another rotates with the drum to measure the temperature variations along the radial and circumferential direction respectively. Experiments have been performed with various materials such as Quartz sand (0.2 mm) and Glass beads (0.7 mm) to measure the effect of filling degree and rotational speed on mixing time and wall-solid contact coefficient. Thermal variations in the bed have been studied thoroughly and it is found that, as the time interval increases the gradients in the bed becomes closer. Contact heat transfer has been investigated from the heat balance between wall and solid. The effect of rotational speed, filling degree on the contact coefficient have been estimated. It shows that as the rotational speed increases, the contact coefficient also increases. The heat transfer measurements show good agreement with the proposed models.