Fabian Herz

HEAT TRANSFER EXPERIMENTS IN A ROTARY DRUM FOR A VARIETY OF GRANULAR MATERIALS

The influence of material properties on the contact heat transfer coefficient between the covered wall surface and the solid bed was investigated. The contact heat transfer coefficients were calculated from the measured radial and circumferential temperature profiles. Experiments were carried out with six different materials, including steel spheres, animal powder, cement clinker, quartz sand, glass beads, and expanded clay. The rotational speeds were varied from 1 to 6 rpm to evaluate the influence of rotational speed on the contact heat transfer coefficient. The measured contact heat transfer coefficients were compared with four models from the literature.

Influence of the Motion Behavior on the Contact Heat Transfer Between the Covered Wall and Solid Bed in Rotary Kilns

The effect of the transverse motion behavior on contact heat transfer was experimentally investigated in an indirectly heated batch rotary drum. Inside the drum, one rotating and one stationary measuring rod were installed, each assembled with 16 K-type thermocouples to measure temperatures. Thus, the radial and circumferential temperature gradients within the solid bed were measured, and the contact heat transfer was determined. As test materials, quartz sand, alumina, and cement powder were used, and the parameters filling degree (10–20%) and rotational speed (1–6 rpm) were varied.

Analysis of Local Heat Transfer in Direct Fired Rotary Kilns

Heat transfer in the rotary kiln is a complex phenomenon due to the different modes of heat transfer. In the first part of this study, the local heat transfer coefficients are analysed theoretically, to describe the heat transfer mechanisms in the cross section of the rotary kiln. Furthermore, the axial solid motion along the length of the kiln is considered in the local surfaces which exchanges the heat. A pilot plant drum of length 0.45 m and internal diameter of 0.6 m has been designed and fabricated to measure the contact heat transfer coefficient from the kiln wall to the covered solid bed. The cylinder is heated continuously by means of three electrical heaters fixed externally around the cylinder at various positions. K-type thermocouples have been used to measure the wall and solid bed temperature along the circumferential and the radial direction. Experiments are performed with various materials such as Quartz sand and Copper pellets of different size, shape and thermal conductivity. The effect of the material properties, the rotational speed (1–6 rpm) and the filling degree (10–20%) on the contact heat transfer have been studied thoroughly.Copyright

Prozessmodellierung von direkt befeuerten Drehrohröfen zur Beurteilung der thermischen Belastung des Feuerfestmaterials

Es wurde ein mathematisches Modell entwickelt, mit dem die axialen Temperaturverläufe des Schüttgutes, des Gases, der Feuerfestauskleidung und des äußeren Rohrmantels in direkt befeuerten Drehrohröfen beschrieben werden kann. Damit sollen auf theoretischem Wege die Bedingungen ermittelt werden, mit denen die Qualität von Produkten verbessert und industrielle Prozesse energetisch optimiert werden können.

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.Copyright