For drying on inert particle surfaces in a fluidized bed, liquids containing solid matter can be sprayed, so that the liquid can be uniformly distributed on the surface of all particles. A mathematical description of the wetting degree in a cylindrical fluidized bed with liquid injection is presented. To characterize the process, a simplified model of the drying with the definition of a wetting degree with an inactive bypass in the fluidized bed is discussed. The validation of the model was ensured by experiments with water injection and variation of injection rate.