Abstract: In order to optimize the drying process of Zanthoxylum bungeanum and reduce energy consumption, the controllable system of hot air coupled microwave drying for thinlayer Zanthoxylum bungeanum was applied to investigate the dehydration characteristics at different hot air temperatures of 55 ℃, 65 ℃ and 75 ℃ and microwave powers of 280 W, 462 W, 595 W. Based on the variation of moisture ratio of Zanthoxylum bungeanum with time, the dynamic model of hot air coupled microwave drying of thinlayer Zanthoxylum bungeanum was determined by solving Ficks second diffusion law and the effective moisture diffusivity (Deff) was calculated. The tissue morphology of outer epidermis of Zanthoxylum bungeanum and the specific energy consumption of hot air coupled microwave drying were compared with that of hot air drying. The results showed that the increase of hot air temperature and microwave power resulted in the acceleration of drying rate of Zanthoxylum bungeanum, and the effect of high microwave power on the internal dehydration of Zanthoxylum bungeanum was greater than that of increasing the hot air temperature to enhance the convection of water on the surface of Zanthoxylum bungeanum. The fallingrate period was the main stage of drying, during which less microwave radiation energy was absorbed by polar water molecules and low moisture diffusivity extending the drying time. The variation range of moisture diffusion coefficient was （1.650 26-4.510 93）×10-8 m2/s. Logarithmic model was selected as the best to predicate the moisture variation of Zanthoxylum bungeanum in hot air coupled microwave drying. The scanning electron microscope (SEM) and energy characteristic analysis showed that, compared with hot air drying, the opening degree of stomatal apparatus in the outer skin of Zanthoxylum bungeanum dried by hot air coupled microwave was significantly greater, the Deff also increased in order of magnitude, the specific energy consumption decreased by 1/9 to 1/5, and the energy efficiency accelerated by 4 to 5 times. The conclusions provide technical guidance for the practical application of Zanthoxylum bungeanum drying engineering and present the theoretical basis for its process optimization, parameter design and energy saving.

Key words: hot air, microwave, drying kinetics, energy consumption, microstructure

摘要： 为优化青花椒干燥工艺，降低能耗，通过实验探究不同热风温度（55℃、65℃、75℃）和微波功率（280 W、462 W、595 W）干燥工况的花椒薄层失水特性；基于水分比随时间的变化，应用Fick第二扩散定律，确定花椒薄层热风微波耦合干燥动力学模型和有效水分扩散率（Deff）；对比分析热风—微波耦合干燥与热风干燥的能耗以及干制花椒外表皮微观结构。结果表明：升高热风温度或增加微波功率，均有利于提高干燥速率，且高微波功率促进花椒内部失水的作用远大于升高热风温度增加花椒表面水分强制对流的作用；在干燥降速期，随着极性水分子吸收微波辐射能量减少，水分扩散率降低，Deff的变化范围为（1.65026~4.51093）×10-8m2/s；Logarithmic模型为青花椒薄层热风微波耦合干燥失水动力学最优模型；相比于热风干燥，热风微波耦合干燥的比能耗减小1/9~1/5，能效增大4~5倍；花椒经热风微波耦合干燥后的外表皮气孔器张开程度更大。研究结果可为实际花椒干燥应用工艺优化、参数设计与节能提供理论依据。

关键词: 热风, 微波, 干燥动力学, 能耗, 微观结构