Numerical performance assessment of a solar greenhouse dryer for the drying of Olive Mill Wastewater
Résumé
Olive Mill wastewater is considered as a hazardous olive by-product due to its high organic load and its toxic activity. The drying of this effluent under a greenhouse dryer can be an interesting low-cost treatment to obtain a high added value product. In order to provide an efficient design of the dryer that can consistently meet the needs of the customers, a numerical model was developed, as a first step before project implementation, to simulate the drying process inside a modified even span solar greenhouse dryer. The governing conservation equations were thus solved using COMSOL Multiphysics. To understand and then control the coupled heat and mass transfer as well as the flow, simulations have been first performed for five typical days of July for the proposed dryer as well as under the open sun. Higher air and OMWW temperatures and better air circulation inside the solar dryer reduced more effectively the drying time needed to evaporate 28.7 kg m−1 from 120 hinder open sun to 90 h inside the tested dryer. The overall efficiency of the studied greenhouse dryer and under the traditional open sun drying reached 68.1 and 50.1%, respectively, after the drying period. The study of the effect of some geometrical and Tunisian climatic conditions on the evaporated quantity showed that separated shallow basins in a greenhouse dryer during July make more effective the drying process and provide significant improvement. The obtained results allowed not only a better understanding of the drying kinetics for both studied drying processes but also an optimization of the dryer design.