番木瓜片热风微波耦合干燥条件及干燥模型建立

Drying conditions and drying model of papaya slices during combined microwave-convective hot air dehydration

为研究番木瓜片采用热风微波耦合干燥的干燥特性和最优工艺组合,选用自制热风微波耦合干燥系统进行实验,得出热风微波耦合干燥曲线、干燥速率曲线及最优工艺组合,并建立干燥模型。结果表明:番木瓜片热风微波耦合干燥速率经历一个短暂的加速期后较长时间处于降速期;番木瓜片热风微波耦合干燥综合效果最优的组合为:热风温度60℃、微波功率密度5.5 W/g、热风风速0.5 m/s,其中微波功率密度对干燥综合效果的影响起主导作用;番木瓜片热风微波耦合干燥动力学模型可用Page方程描述,即M_R=exp(-0.0011T-0.0069P_D+0.073t(^(0.0015T2-0.1993T+7.9642));番木瓜片热风微波耦合干燥有效水分扩散系数介于2.533×10^(-9)~6.0792×10^(-9)m^2/s之间,且有效水分扩散模型为:10^(-10)D_(eff)=0.507T+6.72P_D+10.1v-32。

In order to study the drying characteristics and optimum conditions of combined microwave-convective hot air drying of papaya slices, several test index values, such as colour change, rehydration ratio, drying rate and unit energy consumption during drying process were investigated, and the technological parameters of hot air temperatures, microwave power densities and hot air velocities were optimized. The laboratory-made dryer, having the characteristics of microwave power continuously adjustable and the material heated evenly, was used to do single factor test and orthogonal test for combined microwaveconvective hot air drying. Combined microwave-convective hot air drying curve and drying rate curve of papaya slices were obtained for different technological parameters.The drying kinetics model and effective moisture diffusion model of papaya slices during combined microwaveconvective hot air drying were established. The results showed that combined microwaveconvective hot air drying process of papaya slices consisted of a brief acceleration period and a prolonged deceleration period. Combination drying with hot air temperature of 60 ℃ , microwave power density of 0.5 W/g and hot air velocity of 0.5 m/s was optimal in terms of comprehensive drying index. Microwave power density was the most significant experimental factor in orthogonal test of combination drying.Page model was proved to be more suitable in describing combined microwave-convective hot air drying characteristics of papaya slices, and the equation was：MR = exp（ -0.0011T -0.0069PD ＋ 0.073t（0.0015T^2-0.1993T＋7.9642））. The effective moisture diffusivity was among 2.533 × 10^-9-6.0792×10^-9 m^2/s, and the effective moisture diffusion model of combination drying of papaya slices was： 10-10 Doff =0.507T ＋ 6.72PD ＋ 10.1V-32.