Department of Farm Machinery, College of Agriculture, Isfahan University of Technology, Isfahan, Iran.
J Sci Food Agric. 2013 Feb;93(3):471-8. doi: 10.1002/jsfa.5786. Epub 2012 Jul 17.
The investigation of drying kinetics and mass transfer phenomena is important for selecting optimum operating conditions, and obtaining a high quality dried product. Two analytical models, conventional solution of the diffusion equation and the Dincer and Dost model, were used to investigate mass transfer characteristics during combined microwave-convective drying of lemon slices. Air temperatures of 50, 55 and 60 °C, and specific microwave powers of 0.97 and 2.04 W g(-1) were the process variables.
Kinetics curves for drying indicated one constant rate period followed by one falling rate period in convective and microwave drying methods, and only one falling rate period with the exception of a very short accelerating period at the beginning of microwave-convective treatments. Applying the conventional method, the effective moisture diffusivity varied from 2.4 × 10(-11) to 1.2 × 10(-9) m(2) s(-1). The Biot number, the moisture transfer coefficient, and the moisture diffusivity, respectively in the ranges of 0.2 to 3.0 (indicating simultaneous internal and external mass transfer control), 3.7 × 10(-8) to 4.3 × 10(-6) m s(-1), and 2.2 × 10(-10) to 4.2 × 10(-9) m(2) s(-1) were also determined using the Dincer and Dost model.
The higher degree of prediction accuracy was achieved by using the Dincer and Dost model for all treatments. Therefore, this model could be applied as an effective tool for predicting mass transfer characteristics during the drying of lemon slices.
研究干燥动力学和传质现象对于选择最佳操作条件和获得高质量干燥产品非常重要。本文使用传统扩散方程的解析解和 Dincer 和 Dost 模型研究了柠檬片联合微波-对流干燥过程中的传质特性。空气温度为 50、55 和 60°C，特定微波功率为 0.97 和 2.04 W g(-1)。
干燥动力学曲线表明，在对流和微波干燥方法中，存在一个恒速干燥期和一个降速干燥期，而在微波-对流处理的开始阶段存在一个非常短的加速期外，只有一个降速干燥期。采用传统方法，有效水分扩散系数在 2.4×10(-11)到 1.2×10(-9) m(2) s(-1)之间变化。Biot 数、传质系数和水分扩散系数分别在 0.2 到 3.0（表明同时存在内部和外部传质控制）、3.7×10(-8)到 4.3×10(-6) m s(-1)和 2.2×10(-10)到 4.2×10(-9) m(2) s(-1)范围内确定。
对于所有处理，Dincer 和 Dost 模型的预测精度更高。因此，该模型可作为预测柠檬片干燥过程中传质特性的有效工具。
