In this study, a pilot solar thin-layer dryer was designed and constructed. This dryer was equipped with an air-to-air cross-flow plate heat exchanger. An aluminum plate with a different design was used instead of holes in its surface. The collector, the airflow hitting the absorbent plate and passing through the surface of the pipes embedded on the absorbent plate received thermal energy and transferred it to the dryer chamber. Using the randomize complete design, influence of thickness of product in three levels of 3, 5 and 8 mm, three levels of air velocity of 0.5, 1 and 1.5 m/s and 2 modes with and without the use of heat exchanger on drying time of onion slices was studied. The crop thickness and airflow velocity had a significant effect on reducing the drying time of onion slices and the effect of crop thickness was greater than airflow velocity. However, the heat exchanger did not have a significant effect on drying time and collector efficiency.
