FLUOROPTIC MEASUREMENTS OF THE LOCAL HEAT-TRANSFER COEFFICIENT INSIDETHE ROTATING CONE REACTOR

The rotating cone reactor is a novel reactor type for rapid thermal pr ocessing of solids. This paper focuses on the experimental determinati on of the gas-to-particle heat transfer coefficient. This quantity has been measured for several particle diameters (average size of 150, 28 0 and 425 mu m) and cone rotational frequencies (11.3 and 28.3 Hz). Th e gas-to-particle heat transfer coefficient obtained from these experi ments varied between 280 and 1030 W m(-2) K-1. Experimental parameters which were kept constant in this study were the particle mass flow ra te (5 g s(-1)), the cone geometry (cone top angle pi/3 radians) and th e temperature of the particle feed (280 degrees C). The experimentally determined heat transfer coefficients were represented in dimensionle ss form as a function of the particle Reynolds number. The particle Re ynolds number has been obtained from measurements of the local gas-pha se velocity and the local particle velocity. Analysis of the experimen tal results revealed that the gas-to-particle heat transfer coefficien ts could roughly be represented by the well-established Ranz-Marshall correlation (Rant and Marshall, 1952, Chem. Engng Progress 48, 173) fo r isolated non-rotating particles. The difference between the experime ntally observed particle Nusselt numbers and the theoretically predict ed Nusselt numbers based on the Ranz-Marshall equation is probably due to the influence of particle rotation on the gas-to-particle heat tra nsfer process. Calculations showed that the time in which the particle s lose half of their rotation frequency is typically in the order of t he particle residence time in the rotating cone reactor.