固定床热风干燥模式对荔枝干制特性的影响

Effect of Fixed-bed Convection Drying Mode on Drying Characteristics of Litchi Fruit

摘要:

采用固定物料位置固定热端（模式I）、变换物料位置固定热端（模式II）和固定物料位置变换热端（模式III）三种模式对荔枝果实进行固定床热风多阶段干燥，分别测定了不同物料层（A、B和C三层）物料的热风风速、温度、水分含量、干燥速率、有效扩散系数（Deff）和体积收缩率。结果表明，不同的干燥层物料的热风和温度分布不均匀。经过四阶段共26 h干燥，模式I、II和III中整体样品的水分含量分别为45.70%、42.07%和41.18%。模式I中A层物料的终水分含量为28.44%，显著低于B层和C层样品（p<0.05），Deff为1.48×10-6 m2/s，显著大于B层和C层物料（p<0.05）。模式II各层间物料终水分含量和Deff差异不显著（p>0.05），干燥较均匀。模式III中A层物料的终湿基含水量和Deff与B、C层的物料的相比差异不显著（p>0.05），干燥较均匀，可实现简约操作和规模加工。

Abstract:

Effects of different fixed-bed convection drying practices including fixed position of sample layer (model I), shifting position of sample layer (model II) and shifting hot air flow direction (model III) on the drying behaviors were determined, such as hot air velocity, temperature distribution, moisture content, effective diffusion coefficient (Deff) and volume shrinkage of litchi sample layer A, B and C. Results indicated that both hot air velocity and temperature were non-uniformly distributed within different sample layer during drying. After 26 h of four stages drying, moisture contents of bulk sample of model I, II and III were 45.70%, 42.07% and 41.18% respectively. For the model I, the moisture content and Deff value in sample layer A were 29.4% and 1.48×10-6 m2/s, respectively, which was significantly different from that of sample layer B and layer C (p<0.05). For the model II and III, more uniform drying behaviors were observed. The moisture content and Deff value in sample layer A showed a little significantly difference compared to sample layer B and layer C (p>0.05). Especially for the model III, less operation procedure was achieved, which was feasibility for industrial application.