In this work the experimental performance of a drying module is presented as the first stage in the design of a modular rotary semi-batch drier for vegetables using hot air as a drying agent. The equipment will be made of a series of such modules, each one working as a batch stage where the material is dried up to a certain extent before passing to the next one, where the operation is repeated. Hence, the whole set-up operates in a semi-continuous mode, such that the first module receives the raw material load at regular time intervals, while the last one delivers the dry product. The operation has been modelled in order to calculate the instantaneous value of the drying rate as a function of the air conditions and the material water content. Integration of this equation with suitable heat and material balances provides a complete description of the air and solid properties at any time, which in turn allows the simulation and optimization of the complete set of modules. Experiments with onions, cut in small cubic pieces, have been carried out for constant values of other operating conditions, namely air velocity, particle size, speed of rotation and onion load, to determine the model parameters.