Abstract
The objective of this work, based on a theoretical and experimental study, is to investigate the energy and economic performance of a totally solar drying unit with storage for aromatic and medicinal plants, to satisfy a dimensioning already carried out on a macroscopic scale for an energy request well defined: to dry a quantity of a given agricultural products during 1 day of harvest season, so between September and May, with a heat storage which relays at night. Drying experiments were conducted for spearmint grown in Tunisia. Mathematical formulation of the physical process of this solar drying unit based on conventional heat and mass transfer equations showed a certain agreement with the experimental results under climatic conditions of Tunis (Tunisia). All the experimental drying curves showed only a falling drying rate period. The main factor in controlling the drying rate was found to be the drying air temperature. It was observed that this unit is able to dry more than 2.5 kg of spearmint per day with a moisture reduction efficiency of 70%. It was found that for all the period of harvest, so for 5 months assumed dryer used per year, the payback period is 3.6 years.