TRANSVERSE BED MOTION AND CONVECTIVE MASS -TRANSFER IN ROTARY CYLINDERS .2. WITH LIFTING WEIGHTS

Lifting flights used in rotary cylinders allow the transport of partic les into the gas cross-section and therefore increase both the gas-sol id mass transfer area and the mass transfer coefficient. The cascade c haracteristics, i.e. the lifting flight holdup as a function of the an gular position, can be calculated from force balances and geometric co nsiderations. By defining a normalized flight holdup, we can represent the cascade characteristics in a general dimensionless form, which is assumed to be linear. The average falling velocity and the mass trans fer area of the falling particles can be obtained from the analysis of the height of the fall, assuming free fall. In order to describe the convective mass transfer at the falling particles, an effective veloci ty is defined by combining the velocities of both gas and particles. E xperimental data obtained from drying experiments allow a general corr elation to be fitted for the convective heat and mass transfer at the falling particles. Contrary to the corresponding transfer area, the co nvective mass transfer coefficient is nearly independent of the rotati onal speed.