Drying of Dates Using Multiple Collectors Areas Followed by Equal Drying Areas in a Solar Tunnel Dryer

摘要

A 12 meter long and 2 meter wide tunnel was designed and constructed to analysis the performance of a solar tunnel dryer using multiple drying and collector sections instead of continuous single collector section followed by a single continuous drying section. The area of each solar collector section was 2 × 2 m followed by an equal drying area. Thus there were three drying zones and three collector zones over the entire tunnel base. The drying air was forced from the collector regions (north side) to the drying regions (south side) of the half circled tunnel where the product was dried. The drying temperature could be easily raised by some 5-30 ℃ above the ambient temperature inside the tunnel at an air velocity of approximately 0.25 m/s. The test was conducted with 136.0 kg freshly harvested dates with initial moisture content of 39.98 % (wet-basis). The dates were dried to a final moisture content of 16.80 % (wet-basis) within a day (12 hours). The results indicated that the drying was faster in the multiple collectors zones arrangement followed by equal mul- tiple drying zones than the single continuous collector zone followed by single continuous drying zone. It was possible to reach the moisture content level for safe storage within a day (12 hrs) with multiple collectors and drying areas whereas it required two days (20 hrs) in a single continuous collector and drying areas. The improvement in the quality of dates in terms of color, brightness, flavor, and taste and food value was distinctly recognized than the open air natural drying method.