Motion of carbon nanotubes in a rotating drum: The dynamic angle of repose and a bed behavior diagram

The granular flow behavior of carbon nanotubes produced by the CCVD method in a laboratory continuous inclined rotary reactor and of a catalyst was experimentally studied using a rotating drum. The dynamic angle of repose of the bulk solid and the standard variation of the solid bed surface were determined as a function of rotational speed of the rotating drum and for several filling percentages of the drum. Whatever the carbon nanotube production conditions, the dynamic angle of repose and the standard variation of the solid bed depended only on the filling percentage of the drum. Results were very interesting for practical application to carbon nanotube production in an industrial continuous inclined rotary reactor, because the granular flow behavior was the same during the reaction throughout the length of the reactor and depended only on the reactor filling. A bed behavior diagram based on the drum rotational speed and on the drum filling percentage was also constructed experimentally. The flow behavior of the solid during carbon nanotube production was on the boundary between the slumping and the rolling modes, leading to a good mixing of gas and solid during the reaction and to an improvement of the mass and heat transfer in the bed. (c) 2008 Elsevier B.V. All rights reserved.