In order to optimize the drying process of Zanthoxylum bungeanum and reduce energy consumption,the controllable system of hot air coupled micro wave drying for thin-layer Zanthoxylum bungeanum was applied to investigate the dehydration characteristics at different hot air temperatures of 55 ℃,65 ℃ and 75 ℃ and micro wave 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.
关键词
热风/微波/干燥动力学/能耗/微观结构
Key words
hot air/micro wave/drying kinetics/energy consumption/microstructure
万方数据