单粒莲子热风干燥特性及其干燥动力学

Drying Characteristics and Kinetics of Individual Lotus Seeds under Hot Air drying Process

摘要:

为了提高莲子干燥品质、缩短干燥时间并降低能耗，采用恒温和分段变温两种干燥方式对单粒莲子进行了50~90 ℃恒温和60(2~4 h)~80 ℃变温热风干燥试验，研究莲子表观变化、复水性、干燥能耗及干燥特性，计算不同干燥条件下的有效扩散系数和活化能。试验表明：在恒温干燥条件下，温度越高，干燥时间越短，而莲子色泽、复水性等品质则越差；在分段变温条件下，干燥时间较60 ℃恒温干燥缩短了，但品质均有所提高，60 ℃(3 h)~80 ℃变温干燥莲子的复水性优于60 ℃(2 h)~80 ℃和60 ℃(4 h)~80 ℃变温干燥，为169.41%，单位能耗比60 ℃恒温干燥减少2033 kJ/g。根据菲克第二定律，得到莲子50~90 ℃恒温干燥有效扩散系数变化范围为1.79×10-9~5.83×10-9 m2/s，60 ℃(2~4 h)~80 ℃变温干燥平均有效扩散系数变化范围为2.97×10-9~2.44×10-9 m2/s。由Arrhenius方程建立有效扩散系数与温度的关系，得到莲子水分活化能为28.33 kJ/mol。试验结果为莲子干燥工艺参数优化及干燥设备设计提供参考。

Abstract:

In order to improve the quality of dried lotus seed, shorten the drying time, and reduce energy consumption, hot air drying processes at constant temperatures (50~90 ℃) and stepwise varying temperatures (60~80 ℃) were adopted to dry individual lotus seeds. Changes in the appearance, rehydration characteristics, energy consumption, and drying characteristics of lotus seeds were investigated, and the effective diffusion coefficient and activation energy were calculated. The results indicated that when the lotus seeds were dried at constant temperatures, the drying time decreased with increasing air temperature, but the color, rehydration ratio, and other qualities deteriorated. When drying was conducted at stepwise varying temperatures, the drying time was shortened compared with that at a constant temperature of 60 ℃, and all qualities were improved. The rehydration ratio of lotus seeds dried using a stepwise varying temperature procedure of 60(3 h)~80 ℃ reached 169.41%, better than those of stepwise varying temperature processes of 60(2 h)~80 ℃ and 60(4 h)~80 ℃, and the unit energy consumption decreased from 14022 kJ/g to 11989 kJ/g compared with that of hot air drying at a constant temperature of 60 ℃. According to Fick’s second law, the effective diffusion coefficient of hot air drying at constant temperatures (50~90 ℃) ranges from 1.79×10-9 to 5.83×10-9 m2/s, and the average effective diffusion coefficient of hot air drying at stepwise varying temperatures ranged from 2.97×10-9 to 2.44×10-9 m2/s. The relationship between the effective diffusion coefficient and temperature was established using Arrhenius empirical formula, and the activation energy value of lotus seeds was calculated as 28.33 kJ/mol. The experimental results provide a valuable reference for the optimization of process parameters for drying lotus seeds and the design of drying equipment.