This paper presents a model of indirect solar dryer augmented with pebble bed thermal storage. The thermal storage system was considered to be placed inside the drying chamber above the 47°-tilted air solar collector and below the crop bed, where an average September-daily insolation profile was given for the 32°N location. A presented mathematical model took into consideration the pressure and natural buoyancy forces, employed the basic governing equations, atmospheric-air psychometric-chart relations, and published correlation relationships. A “QBASIC” computer program was written based on the trial and error method for calculation of different parameters. Dimensions of the dryer system, position and characteristics of the crop and storage beds, strongly affected the behavior of the dryer system, for both rice and tomato products. Referring to the considered indirect solar dryer design type, on the average two and five days were required for rice and tomatoes long-term drying, respectively. This seems to be visible in rice products, however, it is far from applicability for tomatoes mass-drying process in agricultural fields, due to its high initial moisture content.
Air collector applications; Indirect solar dryers; Rice and tomatoes preservation; Natural hot air flow; Natural buoyancy forces