73C-27 |
Heat and mass transfer analysis for a new film drying technique |
H. FENG, Dept. of Food Science & Human Nutrition, Univ. of Illinois, Urbana-Champaign, W. Pennsylvania Ave., Urbana, IL 61801, B. Abonyi, Washington State Univ., Pullman, WA, J. Tang, Biological Systems Engineering, Washington State Univ., Pullman, WA 99164-6120, and C. G. Edwards, Food Science & Human Nutrition, Washington State Univ., Pullman, WA 99164-6376. Refractance Window (RW) drying is a new film drying method for producing dried products from liquid and semiliquid foods. In operation, foods are applied in a thin film on a Mylar belt that moves over a hot water flume. The thermal energy from hot water is transferred through the Mylar belt to remove moisture in the product. Results from our previous studies demonstrated that RW dried products had qualities comparable to freeze-dried counterparts. Energy efficiency measured from a pilot-scale RW dryer was also comparable to other drying methods. Further studies are, however, necessary to understand the mechanism that governs the drying performance of a RW dryer in order to better control product quality and further improve energy efficiency. The objectives of this study were to 1) develop a drying model for Refractance Window drying based on heat and mass transfer analyses, and 2) validate the model with experiments. An energy balance equation was developed over a control volume for product in unit width. The convective and radiative heat transfers from hot water to the product were considered. The condition through the Mylar film was also included in the energy analysis. The mass transfer in the product during the drying process was assumed to be solely controlled by diffusion. The resulting drying equation was solved using the finite difference method. The model prediction of moisture content was in good agreement with experimental results. The temperature prediction was close to that measured with infrared thermometer. Simulation results showed that product film thickness and hot water temperature significantly affected drying rates. The effect of the product thickness on product temperature was, however, negligible under the tested conditions. The developed drying model can be used to guide the design, operation, and modification of RE dryers in improving product quality and increasing energy efficiency.
Session 73C, Food Engineering: Transport Processes and Kinetics
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