Continuous Operation of A Ball Dryer.
ARMY NATICK RESEARCH DEVELOPMENT AND ENGINEERING CENTER MA
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THE OPERATION OF A Precision Drying Systems Model 25N ball dryer was optimized for drying frozen vegetable products. The system was fully characterized by completing material and energy balances. The energy was balanced to 95, including losses dues to air leakage, free convection and radiation. The maximum drying capacity of the system is 6.8 kg 15.0 lb water removed from the carrots per hour, or 8.6 kg 18.9 Ib carrot dried per hour from 89 to 10 moisture. The practical conditions to preclude operational difficulties were identified. The ball screw speed was fixed at 1.2 RPM to maximize residence time. The maximum inlet temperature is limited to 110 C 230 F due to ambient humidity. The feed rate must be less than 96 g 021 lb per min to prevent clogging. A factorial designed set of experiments was performed to develop an empirical drying model based on inlet temperature, feed rate and exhaust valve opening. The model predicts percent water removal for diced carrots to within 2. The model was extended successfully to whole peas and diced potatoes. Measured dependent properties included final percent moisture, total rate of water removal, rehydration ratio and color. Quality was found to suffer when the final moisture content was less than 15 moisture and freezdrying as the second stage to 2 moisture. An economic analysis of this process shows a 70 decrease in utility costs as compared to freezelrying alone. AN
- Food, Food Service and Nutrition