Artificial drying, using industrial devices (dryers), helps to reduce the residual humidity content in biomass in a relatively short time. Convection is one of the most common mode of drying (referred to as direct drying). Heat is supplied by hot air/gas flowing over the surface of the solid. The heat for evaporation is supplied by convection to the exposed surface of the material; the evaporated humidity is carried away by the drying fluid. Indirect dryers (working by conduction) are more appropriate for particulate and granular materials or for very wet solids; while radiative dryers use various sources of electromagnetic radiation with wavelengths ranging from the infrared to microwaves. In this work, two mathematical models of cross flow and rotary dryers (both convective dryers) have been proposed. Both dryers treat wood chips. The two models allow to calculate the thermal efficiency and residence time of wet solid wood chips, as a function of the residual moisture content, as well as the analysis of the behaviour of the outlet wet solid and drying gas, in consideration of the dryer length and of the feeding material conditions in the dryer. The models have been developed in the Mathcad software environment.