When diffusion inside the solid particles which are dried in a fluidised bed can not be neglected this internal diffusion can be accounted for by two mechanisms: (a) the long term response which describes the gradual build up of a concentration profile inside the solid particles as function of the total drying time, and (b) the short term response which describes the generation of a thin concentration boundary layer inside the particles during the passage of these particles through the cloud of a rising bubble. Both mechanisms can be analyzed separately and are included in a final model which can be conceived as a further development of the model presented in Part I.