Testing of the performance of a fruit and vegetable solar drying system in Iraq

In this work a drying system was constructed, consisting of three parts (solar collector, solar drying cabinent, and air blower). Two identical air solar collectors having V-corrugated absorption plates of two air passes, a single glass cover was used. The total area of the collectors is 2.4 m2. The dimensions of the drying cabinet are 1 × 0.33 × 2 m (width, depth, and height). The cabinet is divided into six divisions separated by five shelves. The distance between the shelves is 0.3 m except the upper one, which is 0.5 m from the roof. Each shelf is 0.95 × 0.3 m and is made of metallic mesh. The drying chamber walls are made of aluminum plate except the southern side, which was fixed with glass plate having the dimensions 1 × 2 × 0.002 m. Two types of fruit and one type of vegetables were dried during the present work. These were grapes, apricots, and beans. The moisture content of apricot was reduced from 80 to 13% within one day and a half of drying. Moisture content of grapes was reduced from 80 to 18% in two and a half days of drying, while that of beans was reduced from 65 to 18% in one day only. The results show that the most effective factor on the drying rate is the temperature of the air inside the cabinet. The effect variation of speed of air inside the drying cabinet is small and can be neglected. The relative humidity of air exit from the cabinet was small between (25–30%) and therefore there is no need for high velocity air inside the cabinet.

Through the conducted experimental work, the conclusions that may be drawn are 1) The drying chamber operates at an efficiency of 20% when drying 10 kg of grapes while it operates at an efficiency of 33% when drying 10 kg of apricot in accordance to equation (17). 2) Drying foods in small quantities (thin layer) does not need the passage of rapid airflow. 3) The best drying results for grapes are obtained at 65°C, 0.3 m/s speed of air, and 30% relative humidity within the chamber. While the corresponding results for apricot are obtained at 60°C, 0.3 m/s speed of air and 25% relative humidity. 4) Apricot and grapes need more thermal energy for drying than that computed by the equation (14). Since the type of material is not taken into account in deriving equation (14). 5) Apricot and grapes has retained its vitamin content and nutritional value. This was confirmed by Central Organization for Standardization and Quality Control. This is an advantage in comparison with the chemically treated material. 6) Observing the results, one may conclude that the used solar drier can dry about 10 kg of apricot in a day and half and 10 kg of grapes in two days and a half.