基于果壳孔隙率测定的荔枝干燥仿真

Simulation of Litchi Drying Based on Its Shell Porosity Determination

摘要:

针对荔枝干燥性能受果壳孔隙结构制约问题，通过电镜观察了果壳不同表面的孔隙形态，应用Image Pro软件，计算了其平均孔隙率。通过构建荔枝多层结构水分高温蒸发与热质传输耦合模型，采用Fluent软件，仿真了荔枝70℃干燥过程温度、压力、速度的变化，并比较了该过程的水相体积分数仿真结果与试验值差异。结果表明：荔枝果壳各表面孔隙结构存在自相似性，其平均孔隙率为0.516±0.032；荔枝干燥失水，果体温度由果壳向内传导，渐近平衡；果壳内表面形成逐渐增大的负压差；果肉表面水蒸气速度低，压差小，随时间增加，水蒸气速度及压差波动均增大；仿真结果与试验值能较好对应。

Abstract:

Aimed at the problem of litchi drying performance is restricted by its shell pore structure, each side of the shell pore shape was observed by electron microscopy and its average porosity was calculated by Image-Pro software. Through building a model of water evaporation at high temperature, heat and mass transfer coupling for litchi multi-layer structure, using the Fluent software to simulate the temporal variations of temperature, pressure and velocity in litchi drying process, the difference between simulation result of water volume fraction in this process and experimental value was compared. The results show that the pore structure exists a self similarity in each surface of litchi shell, average porosity is 0.516±0.032; when litchi is dehydrated at 70℃, temperature of the fruit body conducts from shell towards its interior and reaches the equilibrium state gradually; a negative pressure is gradually increasing on its inner surface; water vapor on the flesh surface is with low velocity and small pressure difference, but with the time increase of loss water, the fluctuation of vapor velocity and differential pressure increase too. It’s showed that the simulation result can be better corresponded with the experimental value. These research results would provide a reference for other multi-layer structure fruit drying process.