Comparison of the Performance of a Compatible and Simple Collector In Solar Dryers (Case Study: Grape Dryer)

The application of solar energy and sun dryers in food drying is increasing. Low efficiency is the main problem of this apparatus. To solve this problem, a new heat collector and drying chamber were made and assessed. The cover of the collectors was double glazed and consist of many slats and assembled in such a way that it formed a stair step fashion and made many slots through which inlet air was sucked into the collector to reduce total heat loss. The theoretical and practical efficiency of the dryer was calculated during the grape drying. The thermal efficiency of the new 10-step collector and control at low ambient wind speeds was calculated to be 65% and 56%, respectively. Increasing the ambient wind speed to 10 meters per second and more reduced the thermal efficiency of the matching collectors to 35%. The use of the new collector is recommended only if the ambient wind speed is less than 1 meter per second. The drying time of grape in the solar dryer was significantly - around %108 - shorter than that at similar time for the sun-drying method. The time required for fruit drying in the middle tray was 10 to 14 hours longer than that in other trays. In terms of overall acceptance, the raisins produced at different trays of solar dryer had a similar quality, but all were significantly superior to the traditional (sun-dried) product.