Transverse bed motion and convective mass transfer in rotary cylinders .2. With lifting weights.

Lifting flights used in rotary cylinders allow the transport of particles into the gas cross-section and therefore increase both the gas-solid mass transfer area and the mass transfer coefficient. The cascade characteristics, i.e. the lifting flight holdup as a function of the angular position, can be calculated from force balances and geometric considerations. 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 transfer 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 velocity is defined by combining the velocities of both gas and particles. Experimental data obtained from drying experiments allow a general correlation to be fitted for the convective heat and mass transfer at the falling particles. Contrary to the corresponding transfer area, the convective mass transfer coefficient is nearly independent of the rotational speed.